Ceramic burner heads having passages through which the fuel and combustion-sustaining agent, both generally in gaseous form, as fed can be used as fluid heaters are described, for example, in German patent document (printed application-Auslegeschrift) DE-AS No. 23 47 934. In this burner head combustion air is distributed by a manifold to passages perpendicular to the air flow while a plurality of parallel flow passages conduct the combustion gas (fuel) through the burner head, the system being so constructed that directly ahead of the entry of the fuel gas to the combustion chamber, mixing of the fuel with the combustion air occurs.
Such burner heads are relatively costly especially when the passages for the combustion air are enlarged to ensure a uniform distribution of the fuel gas in the oxidizing agent and hence a broad combustion front.
A burner head for high outputs is described in German patent document (printed application-Auslegeschrift) DE-AS No. 20 44 813. In this head a plurality of parallel flow passages for the fuel gas and the oxidizing medium are disposed adjacent one another so that the flow passages for the oxidizing medium are surrounded by the flow passages for the fuel. It is difficult and complicated to provide this system with the manifolds necessary to distribute the fuel gas and combustion-sustaining gas to the respective passages. Thus, while the supply of the oxidizing agent can be effected through a distribution chamber, the connections for the flow passages for the fuel must be specifically provided in complex and precise configurations, thereby rendering the mounting, assembly and repair costs prohibitive.
High outputs, moreover, require a preheating of the oxidizing agent and the fuel gas. Thus in German patent document (open application-Offenlegungsschrift) DE-OS No. 27 06 043, the gas mixture of the fuel gas and the oxidizing agent, prior to entry into the combustion chamber, and contacted with a recuperative heat carrier whose temperature is raised by contact with the exhaust gases discharged from the combustion chamber.
The literature also describes, see German patent document (open application-Offenlegungsschrift) DE-OS No. 24 08 542, a preheating of the combustion air before it is mixed with the fuel gas in a system in which the combustion air acts as a coolant for metal walls of the combustion chamber. While this system provides an increased efficiency it is frequently desirable to heat the fuel gas as well before it is mixed with the oxidizing agent or medium.